1. Field of the Invention
This invention relates to kinetic energy projectiles, and more particularly to kinetic energy projectiles for defeating reactive armor.
2. Description of the Related Art
There exists an ongoing evolution of both the armor used on armored vehicles (e.g., tanks and armored personnel carriers (APC""s)) and the projectiles used to defeat such armor.
Common anti-armor projectiles of the type fired by tank guns and artillery are typically divided into high explosive and kinetic energy subgroups. High explosive anti-tank (HEAT) projectiles typically include one or more shaped explosive charges which, upon detonation in close proximity to the armor, cause a concentrated jet to penetrate the armor. Common kinetic energy projectiles make use of a long rod penetrator to punch a hole through the armor. As implied by its name, the long rod penetrator includes an elongate, dense, heavy penetrator body or core having a relatively small cross-section. Upon impact with the armor, this small cross-section provides a concentration of impact force on the armor effective to penetrate the armor. Long rod penetrators are typically utilized in armor-piercing fin-stabilized discarding sabot (APFSDS) ammunition.
To defeat modern anti-tank projectiles, explosive reactive armor (ERA), also known as reactive armor (RA) and reactive explosive armor (REA), has been developed. Various ERA forms are disclosed in U.S. Pat. Nos. 4,867,077, 5,577,432, 5,413,027, 5,370,034, and 4,981,067, the disclosures of which are incorporated herein by reference in their entireties. Most ERA is modular, with individual modules formed as xe2x80x9cboxesxe2x80x9d which are typically rectangular prisms but may be otherwise formed. Each ERA box typically includes: an outer layer or plate (xe2x80x9cface platexe2x80x9d) of steel, facing generally outward from the vehicle; a layer of explosive inboard thereof; and an additional layer or plate (xe2x80x9crear platexe2x80x9d) of steel inboard of the explosive. The ERA boxes are arrayed over the surface of the vehicle to be protected and may be directly in contact with the basal armor of the vehicle or may be held slightly spaced-apart from the basal armor.
When a rod penetrator impacts ERA, contact between the penetrator and the outer plate produces a shockwave which detonates the explosive layer. The explosion drives the outer plate further outward. Where the outer surface of the outer plate is not normal to the impact trajectory of the projectile, contact between the outer plate and the projectile produces a deflecting force on the projectile, deflecting both its orientation (defined by its longitudinal axis) and its subsequent trajectory (defined by the path of its center of mass) away from normal to the basal armor. Initially, the impact may bend the penetrator proximate its fore end. The penetrator will typically penetrate the outer plate producing a hole therein. Such penetration does not end the interaction between the outer plate and the projectile. A side of the penetrator will remain in contact with a side of the hole in the outer plate as the penetrator continues inward toward the vehicle and the plate continues outward. The result is a continued deflective force on the penetrator normal to its impact trajectory.
If applicable, a rear plate of the ERA may be driven backward (toward the basal armor) by the explosion. This further enhances deflection since the movement of the rear plate will have a component normal to the impact trajectory. Thus, upon penetration of the face plate and engagement with the rear plate, this relative movement will continuously expose new material on the rear plate to the already deflected penetrator fore end. This further deflects the projectile and provides a potentially greater dissipation of projectile kinetic energy than if the rear plate were simply affixed flat against the basal armor. When the penetrator finally reaches the basal armor, its trajectory has been deflected further off normal to the basal armor and its tip bent yet further off normal so that the projectile is more likely to deflect off the basal armor or attack such a large area of the basal armor that the penetrator will not cause penetration of the basal armor.
Accordingly, in one aspect the invention is directed to an ammunition system featuring a subcaliber kinetic energy penetrator having first and second portions. The first portion preferably represents between about 9% and about 15% of the penetrator mass while the second portion is heavier, is positioned aft of the first portion, and is frangibly coupled thereto. The first portion is preferably tungsten-based while the second portion is preferably uranium-based. The former is chosen to produce a relatively wide hole in the face plate of explosive reactive armor while the latter is chosen to best perforate basal armor. The connection between the two portions is configured to rupture under pre-determined conditions, namely at a threshold torque between the first and second sections. Such rupture reduces the tendency of interaction forces between the armor and the first portion from deflecting the second portion into an ineffective, highly oblique relation to the basal armor.
An exemplary second section length is between 400% and 700% of the first section length.
The penetrators of the invention may be utilized with a variety of known sabot structures including push and pull type sabots. In a push-type sabot, propellant gases are substantially trapped behind a sealing flange or other protuberance located relatively aft along the projectile and typically aft of an additional flange. In a pull-type sabot, the sealing flange is relatively forward along the projectile and may be ahead of an additional flange or feature which helps maintain the projectile centered within the tube. Exemplary push-type sabots are disclosed in U.S. Pat. Nos. 5,155,295 and 5,359,938 while an exemplary pull-type sabot is disclosed in U.S. Pat. No. 5,063,855. The disclosures of these patents are incorporated herein by reference in their entireties. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.